Double Disk Diffusion Test

A test performed to detect inducible clindamycin resistance. Certain strains of Staphylococcus aureus bacteria with natural resistance to erythromycin are placed in vitro in agarose gel. Two paper discs containing Eyrthromycin and Clindamycin are placed about 20 mm apart, in the center of the plate. If a 'D' shape is formed around the Clindamycin Disk than the isolate is reported as resistant to Clindamycin. This occurs due to Erythromycin inducing the bacteria's ERM (B) gene, and thus making it Resistant to Clindamycin.<http://www.parn.org.pk/index_files/D.test.html>